如何从 Map 中检索值<arraylist<string> , 对象&gt; </arraylist<string>

Question

I want to know how can I retrieve values from Map<ArrayList<String>, Object> Where the String and object are stored as Array [] for user define length.

Here is an Example:

                             int counter=0, n=0;

                              if (dataSnapshot.exists()){

                                for (DataSnapshot ds: dataSnapshot.getChildren()){

                                    loca[counter]= new ArrayList<>();

                                    itemListProduct[n]= new ItemListProduct();
                                    itemListProduct[n]= ds.getValue(ItemListProduct.class);

                                    loca[counter].add(testHeaderlist.get(counter));

                                    System.out.println(ds.child("item_NAME").getValue(String.class));

                                    objectMap.put(loca[counter],itemListProduct[n]);

                                    counter++;
                                }

Here the testHeaderlist is an ArrayList<String> where there are some string stored. I wanted to store data in the below Image manner:

So now my question is how can I retrieve the Key as well as the Object from "dataList". As from the code which I have shared at the TOP "n" number of list, and the object are stored in the dataList.

The thing is that I want to retrieve to use it in ExpandableListView. loca as header and itemListproduct as my value Object. Where the both are stored at objectMap .

Can anyone please solve it. Thank you!

Answer 1

It is permitted but rather atypical to have an ArrayList as a key to a map. To get the Object you need to do the following:

Object val = map.get(arrayList)

Here, arrayList must contain the exact same strings in the same order as the ArrayList key which refers to the desired object.

Example

Map<List<String>, Integer> map = new HashMap<>();
List<String> key = List.of("abc", "efg");

map.put(key, 20);
Integer v = map.get(List.of("efg","abc")); // different key so
                                           // object not found
System.out.println(v); // prints null

v = map.get(List.of("abc", "efg"));
System.out.println(v); // prints 20

You can get all the Keys of a map by doing

Set<List<String>> set = map.keySet();

You also need to readup on HashMap and ArrayList to understand how they work. The following will keep replacing the object for the key of list[0]

dataList.put(list[0], object[0]);
dataList.put(list[0], object[1]);
dataList.put(list[0], object[2]);
dataList.put(list[0], object[3]);

When the above is done, list[0] will only refer to object[3]